WIDE-BAND TUNABLE LASER
A tunable laser module having two or more tunable lasers exhibiting different, possibly contiguous or partially overlapping wavelength regions. The lasers are integrated into a single package, thereby extending a total wavelength range for the package that is substantially beyond that covered by a single laser while—at the same time—providing gap-free wavelength range coverage. Of further advantage, the laser module employs a locking mechanism that is relatively immune from backscatter.
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This invention relates generally to the field of tunable semiconductor lasers, and in particular to a wide-band tunable laser module having two or more tunable lasers.
BACKGROUND OF THE INVENTIONTunable semiconductor lasers play a critical role in high capacity, dense wavelength division multiplexed (DWDM) transmission systems that form the backbone of today's optical communications networks. In addition, they are generally regarded as being the preferred transmitters for future optical systems.
SUMMARY OF THE INVENTIONWe have developed, in accordance with the principles of the invention, a tunable laser module having two or more tunable lasers exhibiting different, possibly contiguous or partially overlapping wavelength regions. The lasers are integrated into a single package, thereby extending a total wavelength range for the package that is substantially beyond that covered by a single laser. Advantageously, our laser module may provide the total wavelength range without any gaps.
A more complete understanding of the present invention may be realized by reference to the accompanying drawing in which:
For long haul telecommunications applications wide-band tunable laser modules employing a distributed feedback laser (DFB) have found wide application. An example of such a module is shown in
With reference to that
Shown further in the laser module 100 are two photodiode detectors 155 and etalon 150 which are part of a typical wavelength locking mechanism. In operation, one of the photodiode detectors 155 will serve as a reference photodiode to produce a photocurrent proportional to the laser chip facet power. The second photodiode detector is an Etalon photodiode and produces a photocurrent related to wavelength (frequency).
Co-packaging the laser 110, wavelength locking arrangement 140, modulator 170, and associated components (Power Monitor, Variable Optical Attenuators (VOA), and temperature control circuitry) provide significant opportunity for cost reduction. Despite such advantages however, prior art laser modules 100 only include a single laser and therefore provide only a limited emission range covering, for example, only the C or L band necessary for present day transmission systems.
As shown in this
As can be readily appreciated by those skilled in the art, our inventive structure(s) depicted in this
Of further significance, such a laser module 200 will advantageously offer a much broader output spectrum than is possible with only a single laser chip. In this example, the module 200, may be tuned to provide wavelengths throughout the C-band and L-band(s) (and/or others)—in sharp contrast to the Prior Art. Additionally, and as a further function of its flexability, such a wide-band module may provide it output without any wavelength gaps, thereby minimizing the number of distinct modules that must be employed for a particular application resulting in significant inventory reductions.
While we have only explicitly discussed providing the wavelengths throughout the C-band and L-band(s), it is important to note that our invention is not so limited. More specifically, other bands, (i.e., S-Band) or combinations thereof are certainly possible and contemplated with our inventive teachings.
Still further, it is important to appreciate that our inventive module(s) are not limited to only two laser chips such as those shown in
At this point it is notable that when one passively combines lasers there is associated with such combining a loss, i.e., 3 dB. While this may not be significant when considering only 2 lasers, a 6 dB loss associated with the combination of 4 lasers may be unacceptable. Advantageously—and according to the present invention—when these multiple lasers are combined using an active switch (such as the integrated Mach-Zehnder disclosed herein) the losses are substantially eliminated.
Of particular advantage, by packaging two or more tunable lasers with different, possibly overlapping wavelength regions into a single package—according to the present invention—the overall total wavelength range is extended beyond that possible with a single laser. In addition, the multiple lasers may share optical elements, driving circuitry and control electronics.
Of still further advantage is that a module constructed according to our inventive teachings permits the independent manufacture of relatively narrower-band tunable lasers—which are easier to manufacture—and combine them into a wide-band tunable laser. As can be appreciated, no moving parts are necessary thereby increasing the reliability and manufacturability of our inventive device(s).
Shown in this
As noted before, an important aspect of our inventive structure is that it permits the sharing of a wavelength locking arrangement among the multiple lasers that comprise the overall module. With simultaneous reference now to
Shown in
Interconnecting the PLC with the lasers is a set of free space optical components, including lenses (LENS), isolators (ISO) and wavelength locking arrangement having a pair of detectors (D) and an Etalon (ET). As noted earlier, the two detector may be advantageously used with one of the detectors monitoring the power of the laser light while the other can measure the power of the laser light passing through the etalon. The laser light is directed to the detectors by one or more prisms, positioned within the optical path.
As can be appreciated, since only one of the lasers is active at a particular time, the entire locking system may be shared among the lasers, thereby reducing the overall cost of the module. In addition, while we have only shown and discussed the invention including two individual lasers, it should be readily understood that our invention is not so limited, More particularly, it is understood that three, four or more lasers may be advantageously integrated into a common module, thereby permitting even greater overall cost reduction from sharing common components (wavelength locking arrangement, power, control circuitry, etc) while providing a single module that provides even wideroutput wavelength range(s).
Even further variations in configuration are possible with our inventive principles, as illustrated in
A variation on this configuration of
Still further variations in our inventive structure(s) are shown in
More specifically, the frequency locking system may be integrated onto a common chip 650, which may further include a coupler/switch arrangement. As shown in
As should now be apparent to those skilled in the art, by packaging a plurality of individual lasers having two or more (possibly) overlapping wavelength regions into a single package, the total wavelength range of the integrated package may advantageously be substantially wider that that provided by a single laser. The co-packaging provides additional opportunity to share driving, power and other electrical circuitry, as well as optical locking mechanisms. Finally, since sharing optical components among the lasers is promoted, new, non-conventional locking mechanisms may be employed since their individual cost is marginalized.
Consequently, such integrated modular packages will lead to simplified provisioning and maintenance by service providers. Still further, reduced inventory resulting from modules exhibiting wider applicability only further enhances their attractiveness.
At this point, while we have discussed and described our invention using some specific examples, those skilled in the art will recognize that our teachings are not so limited. More specifically, while we have described devices and modules that are tunable to potentially any wavelength within the C+L+S band(s) without requiring significant development, it is understood that additional band(s) or wavelengths may be provided by such a common module(s), by appropriate selection(s) of the component laser(s). Accordingly, my invention should be only limited by the scope of the claims attached hereto.
Claims
1. A laser module comprising:
- two or more lasers for generating laser light;
- a set of optical components for operating upon the generated laser light prior to its output; and
- a locker, for monitoring and locking the characteristics of the laser light to be output;
- CHARACTERIZED IN THAT:
- the locker is shared between the two or more lasers.
2. The laser module of claim 1:
- FURTHER CHARACTERIZED IN THAT:
- the locker is not in a direct optical path of the laser light to be output.
3. The laser module of claim 1, wherein said locker comprises:
- a splitter, for splitting the generated laser light and directing it into two or more distinct optical paths;
- an etalon positioned in one of the distinct optical paths;
- a photodetector, positioned in the optical path containing the etalon, for monitoring the wavelength of the generated laser light;
- and
- a second photodetector, positioned in another optical path, for monitoring the power of the generated laser light.
4. The laser module of claim 3, further comprising a switch/combiner for switching/combining the generated laser light into a single output.
5. The laser module of claim 4 wherein said switch/combiner comprises a Mach-Zehnder Interferometer switch.
6. The laser module of claim 5 wherein said locker is positioned in an optical path optically coupled to a particular path of the switch/combiner, and an output of the module is within a different optical path of the switch/combiner such that the switch/combiner may selectively switch generated laser light between the locker and the output, as desired.
7. The laser module of claim 6 further comprising an integrated planar lightwave circuit (PLC), said PLC including:
- the locker; and
- an integrated coupler/switch for selectively coupling/switching the generated laser light between the locker and an output as desired.
8. The laser module of claim 7 wherein the PLC is an InP device.
9. The laser module of claim 8 wherein the integrated frequency filter includes a Mach-Zehnder filter.
10. The laser module of claim 9 further comprising one or more lenses, positioned in an optical path between the PLC and an output of the module.
11. The laser module of claim 10 further comprising common driving electrical circuitry, shared among the two or more lasers.
Type: Application
Filed: Dec 31, 2005
Publication Date: Jul 5, 2007
Applicant: LUCENT TECHNOLOGIES INC. (MURRAY HILL, NJ)
Inventors: PIETRO BERNASCONI (EATONTOWN, NJ), CHRISTOPHER R. DOERR (MIDDLETOWN, NJ), DAVID NEILSON (OLD BRIDGE, NJ), JOHN SIMSARIAN (CRANFORD, NJ)
Application Number: 11/306,541
International Classification: H01S 3/098 (20060101); H01S 3/10 (20060101); H01S 3/13 (20060101);